Fractionator with plastic spinning band



March 1963 A. G. NERHElM 3,080,303

FRACTIONATOR wrm PLASTIC SPINNING BAND Filed April 2, 1958 2 Sheets-Sheet 1 INVENTQii March 5, 1963 A. G. NERHEIM 3,080,303

FRACTIONATOR WITH PLASTIC SPINNING BAND Filed April 2, 1958 2 Sheets-Sheet 2 J j 1 .Z 46"; 49

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United States Patent Ofitice 3,986,3d3 Patented Mar. 5, 1%?13 ensues? FiRACTlfiNATGR Wltil ll PLASTHZ Sl ll lldlNG BANE? Arvie Glenn Net-helm, Crown Point, Ind, assiguor to Standard Oil Company, Chicago, 3th, a corporation or Indiana Filed Apr. 2, 19553, Ser. No. 725,358 8 llaims. (Cl. 292-453) This invention relates to improved iractionator columns of the type known as spinning band columns. More particularly, the invention relates to spinning band con-structions for such a fractionator.

in a spinning band column, the complete unit cornprises in general a still pot for holding the charge, a fractionating column or tube, a condenser system, a liquid product receiver, and a rotatable element disposed within the fractionating column. Controllable heating means are provided for supplying heat to the still pot, the still pot and heating element ordinarily being enclosed within a vacuum fiasl: whic is rernovably seated at its upper end in contact with a vacuum jacket which substantially encloses the fractionating column and take-oil line. Throughput in a spinning band column is conventionally controlled by controlling the heaters; however, it has been found that column e'fficiency may be increased by increasing the rotation speed of the spinning band. However, if vibration occurs in spinning band columns and if frictional heat of rotation is generated, the efiiciency is lower.

it is, t erefore, an obiect or" my invention to provide a spinning band column construction which may be 011- erated at high throughputs without loss in eiiiciency. it is a further object of the invention to provide a driving head for a spinning band column and a band shaft con struction adapted to obtain efficient fractionation with band rotations up to 6,609 rpm. Still another object of the invention is to provide a distillation apparatus which is capable of a wide range of operating conditions adapted to meet the needs of individual distiilations.

Many investigations have shown the outstanding characteristics of spinning band columns to be (1) low pressure drop, (2) low operating holdup, (3) low HETP (height equivalent to a theoretical plate), and (4) high eificiency as compared to packed columns.

These features of spinning band columns apply also under vacuum operation but vacuum seals are difficult to maintain with equipment incorporating moving parts. ltis, therefore, an object of my invent-ion to provide a means for driving a spinning band within a iractionator column. It is a further object to provide such a means which is rug ed, is easy to fabricate, and is adapted for use on glass columns.

The above and other objects of the invention will become apparent as the detailed description thereof proceeds.

conventionally, spinning band columns of the type to which my improvements relate employ a rotatable element comprising a metallic band having a cross-sectional area which is substantially less than the flow area the column. Briefly, according to my invention, the conventional band is replaced by a non-metallic or plastic having a core of substantial cross-sectional area with respect to the column flow area. A preferred material is tetr iuoroethylene resin (sometimes known as Teflon), or Kel-F, polyethylene, nylon, polyurethanes, or the like.

The configuration of sucn plastic band is significant. A preferr d form is a mold-bladed element having a core of substantial volume. One such element has a cross section of a square with concave sides, the edges of bladed element having serrations which are uniformly inclined on the blade edges.

The multi-hladed bands have many points of contact with the column wall and are more stable than the twoedged bands having only two points of contact and me less subject to vibration. The mult-i-bladed bands, designed according to my invention, are more efficient.

An optimum rotation speed for the spinning band is a compromise between efficiency increase due to increased mixing at higher rpm. and equilibrium upset due to e' cess heat caused by band friction at higher rpm. A four-bladed band having more contact surface generates more frictional heat. Consequently, such a band has a lower optimum rpm. than a three-bladed band and as the number of blades is reduced, less heat is generated. However, as the number of blades is reduced, the adverse elfects of less contact of the vapor and liquid as well as less effective mixing of the two phases are encountered.

An important feature of my invention is that the larger number of blades and larger band core leave less free space within the column so that the vapor molecules have a shorter lateral path to travel in making contact with the liquid phase on the column wall. Thus, moderate throughputs with the four-bladed band are most efficient.

On the other hand, with the three-bladed band, higher r.p.rn.s may be used as low throughputs to attain fractionating efficiency.

One way in which the spinning band can be fabricated according to my invention is to thread a rod of round cross section and then cut away symmetrically spaced grooves in the round faces of the rod to provide radial blades having threaded Wiping edges extending radially rom a substantial root or core. If desired, the band may be made of short sect-ions and threaded upon a supporting shaft or tube. Two or three-bladed short sections may be staggered with respect to adjacent sections so as to provide symmetric wall contact over the length of the column.

However constructed, the multi-bladed large cored. spinning band is mounted so as to place the blade edges in close running lit with the interior of the column wall. Advantages of this type of spinning band include a low holdup of liquid and low pressure as well as giving low HETP values which are from /2 to /3 lower than the HETPs for spinning band columns employing conventional metallic rotatable elements.

Further details and advantages of my invention will become apparent as the description thereof proceeds with reference to the accompanying drawings werein:

FEGURE l is a vertical section showing the improved spinning band drive, head construction and distillation flask;

FIGURE 2 is a schematic showing of the drive shaft and spinning band to be employed in the apparatus or" FIGURE 1;

FIGURES 3 and 4 are isometric and end views, respectively. of a section of four-bladed band;

FlGURE 5 is a fragmentary elevation of the band in a column;

FlC-URES 6 and 7 are isometric and end views of another embodiment of the spinning band design;

FIGURES 8 and 9 are isometric and end views, respectively, of another modification of the spinning band designed in accordance with my invention;

FlGlJ'itlE 10 is a fragmentary elevation of the staggered band of FIGURE 8; and

FIGURE 11 is a section taken along 11-11 in FIG- URE 16.

Referring to the drawings, a column comprising a relatively long thin glass tube, contains the spinning band it having a drive shaft 12 which extends through the head 13 and is secured to the drive pin 14 within the magnetic coupling 15. The coupling 15 includes a pair of opposed magnets 16 and 1'7 arranged axially of each accuses 3 other and of the shaft 12. The drive magnet 16 is secured, for example, by a chuck. means 18 so that it may be driven, and the other magnet 17 is within a vacuumtight and non-magnetic housing 1d which is fixed to the head 13 by means of a standard tapered joint 29 engaging a corresponding tapered joint 21 in head 13.

The elongated drive pin 14 disposed within the separable housing 19 is arranged to be rotated with the enclosed magnet 17. An antifriction bearing means 22 rotatably supports the drive pin '14 within the housing 19. The drive shaft 12, fixed to drive pin 14, extends longitudinally from the lower end of the housing 19, through the head 13, and engages the band shaft 23 which in turn supports the rotatable element or band 11.

The rotatable band 11 is slightly smaller in its greatest lateral dimension than the internal diameter of the fractionating tube or column 10. Rotation of the closefitting band 11 produces a Wetted Wall effect within the fraotiouating tube 10 with the result that there is intimate contact between the up-flowing vapors within the column 10 and the down-flowing reflux on the Wall. thereof.

The head 13 includes a tapered body 24 arranged in a vacuumatight seal with the. seat 25 at the upper end of the column 10. The head 13 includes laterally-extending condenser inlet 26 and outlet 27, each passing through the side wall thereof and being connected to opposite ends of the looped condenser 28 which depends below the hollow body 24 into the top of the column 10. A drip tip 29'is provided on each of the separate legs of the condenser 28. A vacuum connection 30, also laterally extending from the side wall of head 13, permits vacuum operation of the column 10 and completes the construction of head 13.

The leads 31' to thermocouple 32' pass through the top threaded cap 19a of housing 19 and the thermocouple 32 is disposed adjacent the upper end of the spinning band 11 and soldered in place. The solenoid 33 is aligned with the soft iron core 34 embedded within a cavity Wall 35 or" housing 19. Immediately below the exposed inner end of the core 34 is arranged the upper paramagnetic end 36 of the needle shaft 37 which passes Within the needle guide bore 39 in housing 19 and the needle tip 40 is on the needle seat 41. The needle tip 40 is thus raised from the seat 41 by the action of the electromagnet bar or core 34 on-the paramagnetic top 36 of the needle 37 when the solenoid coil 33 is energized.

The: Teflon spinning band 11 of the most eflective design is illustrated in the drawings. The band shown in FIGURE 2 was fabricated by stringing machined fourbladed Teflon sections 46 on a stainless steel tube 47. The edges 48 of the multi-bladed band 11' are serrated by threading the Teflon rod sections and then cutting away longitudinal grooves to leave the blades 49 as shown in FIGURES 3, 4 and ofthe drawings.

Three-bladed and two-bladed bands are shown in FIG- URES 6, 7, 8 and9 edges 48 being provided with serrations 48a. FIGURE illustrates the use of the twobladed sections of FIGURES 8 and 9 in staggered array and mounted on a tube 47 similar to the band illustrated by FIGURE 2.

The threaded edges 48a are mounted in close running fit with the interior of the column wall 10 and, depending upon the direction of rotation, can be used to alfect the flow of reflux along the column wall and thereby control the-efi'iciency of the vapor-liquid contact within the column. Advantages of my spinning band include a low holdup of liquid and low pressure drop as well as giving low HETP values which are from /2 to /3 lower than the HETPs for spinning band columns employing conventional metallic rotatable elements.

Teflon is preferred because of its m-achinability, resiliency, and ability to operate at high rotational speeds without upsetting vapor-liquid balance within the column. Thus, for a given rotational speed, the spinning band constructed of Teflon is much superior to a metal band such as is conventionally employed.

The self-lubricating properties of Teflon are not relied upon, in fact, this property would be observed only if the Teflon band were allowed to spin within the unloaded column, thereby depositing a film of Teflon on the column wall. In the preferred operation of my column, it is loaded with liquid before the band is spun so that a film of liquid is on the walls of the column and act as :a barrier which prevents the deposition of Teflon on the column wall.

Simply coating a metal band with Teflon does not increase column efliciency over an ordinary all-metal band and does not approach the efliciency of the Teflon band. The Teflon-coated metal band has a greater tendency to run in contact with the column wall to produce a coating which is incapable of maintaining a liquid film which is desirable for fraction'ators of this type.

Data have been obtained which show the superiority of the Teflon band over a metal band, with or without a Teflon coating. These data are set forth in the fol lowing-tables:

TABLE I Theoretical Plates (mm. Columns) Throughput (mL/hr.)

Teflon Band Metal Band Teflon-Coated Metal Band 1 Calculated from performance on 60 mm. column TABLE II Performance at Total Reflux and Atmospheric Pressure Teflon-Coated Metal Band Test N0.

Baud Speed, Throughput Theoretical r.p.m. (ml./hr.) Plates (60 mm.

Columns) The Teflon band column has more theoretical plates at equivalent pressure drop and holdup and since the Teflon band can be operated at increased speeds, the number of theoretical plates in a column and the throughput of a column are substantially increased.

The design of the plastic bands in accordance with my invention is important and as describedv herein, certain shapes have been demonstrated to be unusually efficient. In each instance, however, the large core produces desirable results not attainable with other designs or'materials of construction.

Referring again to FIGURE 1, showing the distillation flask in combination with the spinning band, drive and head construction, flask 5G is pear-shaped and can be set in a cone-shaped heater and insulated for use in distillation operations. The contents of flask 50 are stirred with a Wire impeller 6i fixed to the lower end of spinning band 11. Flask 50 is aligned with and fixed to the lower end of the column 10 by means of flask joint 71. Flask 56 is provided with a thermocouple Well and the thermocouple leads 55 extend therefrom.

The efliciency of the spinning band column has been increased by improving the band design to cause better mixing and contacting and by constructing the band to reduce frictional heat and to decrease wetting of the band.

The higher efiiciency of my spinning band can be dlrectly related to the specific design features. Better mixing and contacting of the liquid and vapor phases results from using a number of blades. These have further enhanced by providing a large core which reduces the length of the vapor diffusion path to increase efliciency and also increase mixing by carrying all the vapor in a long spiral path while more liquid mixing is caused by more blade edges making firm contact with the liquid reflux on the column wall.

Smooth blade rotation results from the stability of more blade in proximity to the column wall. In addition, the use of Teflon reduces the frictional heat even at high band speeds. Furthermore, its resilience and lower density permit smoother and more vibration-fre rotation at high speeds. Another advantage appears to be the low degree of wetting of the Teflon spinning band relative to the high degree of wetting of the column wall by the condensed vapor.

This application is a continuation-in-part of my now abandoned co-pending application Serial No. 596,584, filed July 9, 1956 and entitled Spinning Band Fractionator, which is in turn a continuation-in-part of application Serial No. 507,630, filed May 11, 1955, issued as US. 2,764,534 and entitled Head for Spinning Band Fractionator.

Although the invention has been described with reference to a preferred embodiment thereof, it is to be understood that this is by way of illustration only. Accordingly, it is contemplated that modifications and variations can be made in the apparatus by those skilled in the art in light of the preceding description and without departing from the spirit of the invention.

What I claim is:

'1. In a spinning band fractionation apparatus comprising a distillation flask, a fixed fractionating column connected thereto, a rotatable band disposed within said column, a condenser associated with said column and disposed above said band, means for rotating said band, and take-ofi line means for removing condensed vapors, an improved rotatable band which comprises a multibladed band having a core of substantial displacement volume in said column, and serrations on the edges of the multiple blades,, the edges of said blades being arranged to run close to but spaced from the inner stationary wall of said column.

2. The apparatus of claim 1 wherein the band comprises a plurality of elongated segments threaded over a shaft, each segment having a central core of substantial volume, a bore through said core to accommodate a band shaft, a plurality of blades extending radially of said core, and uniform serrations on the outer edges of said blades.

3. The apparatus of claim 1 wherein the band comprises a non-wetting plastic having a low coeflicient of friction.

4. A band for use in a spinning band fractionator column which comprises a plurality of axially elongated segments threaded over a shaft, each segment having a central core of substantial cross-sectional area, an axial bore through said core containing the band shaft, a plurality of radial blades carried by said core, the outer edges of said blades being substantially parallel to the of the band shaft, and uniform serrations on the outer edges of said blades.

5. The apparatus of claim 4 wherein the said segments comprise a non-wetting plastic having a low coeflicient of friction.

6. A spinning band fractionation apparatus comprising a still pot, a fixed fractionating column connected thereto, a rotatable band disposed within said column, a shaft for said band, means for rotating said shaft, a condenser associated with said column and disposed above said band, take-off line means for removing condensed vapors from the column, said band having a core body of substantial cross section relative to the normal flow area of the column, blades integral with and extending radially from said core body, and serrations on the outer edge of the said blades.

7. The apparatus of claim 6 wherein said core body comprises a series of similar core segments threaded over said shaft.

8. In a spinning band fractionation apparatus comprising a distillation flask, a. fixed fractionating column connected thereto, a rotatable band disposed within said column, a condenser associated with said column and disposed above said band, means for rotating said band and take-off line means for removing condensed vapors, an improved rotatable band which comprises a plurality of axially elongated segments threaded over a shaft, each segment having a central core of substantial cross-sectional area, an axial bore through said core containing the band shaft, a plurality of radial blades carried by said core, the outer edges of said blades being substantially parallel to the axis of the band shaft, and uniform serrations on the outer edges of said blades.

References Cited in the file of this patent UNITED STATES PATENTS 1,466,579 Collver Aug. 28, 1923 2,032,785 Zorn et al. Mar. 3, 1936 2,546,381 Zahm Mar. 27, 1951 2,556,752 Galstaun et al. June 12, 1951 2,573,807 Piros et al. Nov. 6, 1951 2,608,528 Piros et al Aug. 26, 1952 2,695,246 Jurgensen et al. Nov. 23, 1954 2,712,520 Nester July 5, 1955 2,764,534 Nerheim Sept. 25, 1956 2,783,401 Foster Feb. 26, 1957 2,955,990 Smith Oct. 11, 1960 FOREIGN PATENTS 330,805 Great Britain June 19, 1930 656,605 Great Britain Aug. 29, 1951 807,857 Great Britain Ian. 21, 1959 OTHER REFERENCES Baker et al.: A Large Spinning-Band Fractionating Column, from Industrial and Engineering Chemistry, vol. 12, No. 8, pages 468-470, Aug. 15, 1940. 

1. IN A SPINNING BAND FRACTIONATION APPARATUS COMPRISING A DISTILLATION FLASK, A FIXED FRACTIONATING COLUMN CONNECTED THERETO, A ROTATABLE BAND DISPOSED WITHIN SAID COLUMN, A CONDENSER ASSOCIATED WITH SAID COLUMN AND DISPOSED ABOVE SAID BAND, MEANS FOR ROTATING SAID BAND, AND TAKE-OFF LINE MEANS FOR REMOVING CONDENSED VAPORS, AN IMPROVED ROTATABLE BAND WHICH COMPRISES A MULTIBLADED BAND HAVING A CORE OF SUBSTANTIAL DISPLACEMENT VOLUME IN SAID COLUMN, AND SERRATIONS ON THE EDGES OF THE MULTIPLE BLADES, THE EDGES OF SAID BLADES BEING ARRANGED TO RUN CLOSE TO BUT SPACED FROM THE INNER STATIONARY WALL OF SAID COLUMN. 